In the blow molding of plastic bottles, it has long been an objective to produce a bottle with a completely finished base in the blowing step. Earlier methods and apparatuses for producing bottles from tubular parisons have not been completely effective in the removal of the tail from the bottle subsequent to the blowing step. It is often necessary to subject the bottle to a secondary finishing operation to completely finish the base of the bottle. A number of methods and apparatuses have been proposed for severing the tail from the bottle. In U.S. Pat. No. 2,994,103 there is disclosed an apparatus that removes the waste portion from the blown plastic article while the article is supported by the mold. However, to initiate the removal process, the mold must be partially opened. This step requires additional time and results in lower output. The apparatuses described in U.S. Pat. Nos. 3,098,593; 3,172,152; 3,351,981; 3,465,931; and 3,486,190 all require that the article be removed from the mold to a waste removal station. The articles are removed to the waste removal station by a variety of methods, none of which utilize grasping the waste portion. U.S. Pat. Nos. 3,040,376; 3,266,083; 3,417,428; 3,464,084; and 3,506,171 also require that the article be removed from the mold and taken to a waste removal station. However, these patents do make use of the waste portion by engaging the waste to remove the article to the station. All of the above-mentioned patents require either that the article be removed from the mold before removing the waste or that the mold be partially opened before the waste is removed. U.S. Pat. No. 3,363,282 discloses an apparatus for removing the waste from a blown plastic article while the article is still in the closed mold. However, the apparatus does not possess the required versatility for attachment to a variety of different blow molds. The apparatus has to be mounted on the side of the mold cavity which will result in a requirement for more lateral space when the mold is open.
In U.S. Pat. No. 3,910,742, an apparatus is shown which removes the waste portion, e.g., the tail, while the article is retained in the mold. Due to the versatility of this apparatus, it is suitable for use with a variety of existing blow molding machines. The apparatus obtains a hold on the waste portion by means of a pair of opposed grippers having planar gripping faces. A power piston associated with each gripper moves the gripper arcuately downwardly about its pivot point to break and move the gripped waste portion from the article. Each pivot point is located so that it is laterally offset from the planar gripper surface and below the uppermost extent of the gripper surface. By each pivot point being so located, rotation of the planar surfaces about their respective pivot points causes the uppermost extent of the gripper surfaces to move toward one another as they make their downward rotation. This is due to the fact that the distance R.sub.1, from the pivot point to the uppermost extent of the planar gripping surface is greater than the shortest distance, R.sub.2, from the pivot point to the planar gripping surface. (This shortest distance is measured along a horizontal line through the pivot point to the planar surface.) Since R.sub.1 is larger than R.sub.2, that portion of the planar surface measured at R.sub.1 moves along an arc outside of the arc travelled by the planar surface portion at R.sub.2. Thus, the opposed planar surface portions at R.sub.1 move toward each other resulting in a pinching of the waste portion. When the pinching is severe enough, the waste portion is cut at the pinch point, thus disrupting the downward pull necessary to remove the waste portion from the article. Thus, the waste portion is not removed from the article and the article must either be rejected or the waste portion must be removed by a secondary operation. In either case, the economics of operating this type of apparatus is adversely affected.
Therefore, it is an object of this invention to provide an apparatus for completely removing the waste portion of a plastic article while the article is retained within the mold cavity and which apparatus does not sever the waste portion prior to the waste portion being pulled from the article.